Dewey Hodges | Georgia Institute of Technology (original) (raw)
Papers by Dewey Hodges
Two major barriers to widespread US acceptance of offshore wind energy is reliability of rotor bl... more Two major barriers to widespread US acceptance of offshore wind energy is reliability of rotor blades and the difficulty to access for inspection and maintenance. This work presents operation and design strategies aimed to increase blade reliability and maximize power production. Operating strategies that prolong blade life while optimizing energy output allow for smarter maintenance planning and lower maintenance costs. Offshore plants require significant balance of station costs associated with each turbine, leading to large rotor diameters to capture the most energy per turbine. Rotor diameters have already approached 130 m, so this work extends that trend to 100 m blade (205 m diameter) designs. A combined aero/structural optimization process was used to produce new 100 m blade designs. A high-fidelity analysis method is presented to assess the local damage effects of a common damage type. The operation and design strategies are then compared for their effect to mitigate the loc...
Journal of Applied Mechanics, 2015
An asymptotic theory of composite plates is constructed using the variational asymptotic method. ... more An asymptotic theory of composite plates is constructed using the variational asymptotic method. To maximize simplicity and promote efficiency of the developed model, a transformation procedure is required to establish a mathematical link between an asymptotically correct energy functional derived herein and a simpler engineering model, such as a generalized Reissner–Mindlin model. Without relaxing the warping constraints and performing “smart minimization” or optimization procedures introduced in previous work, a different approach is suggested in this paper. To eliminate all partial derivatives of the 2D generalized strains in the asymptotically correct energy functional, a hybrid transformation procedure is systematically carried out by involving modified equilibrium and compatibility equations, and solving a system of linear algebraic equations via the pseudo-inverse method. Equivalent constitutive laws for the generalized Reissner–Mindlin plate model are then estimated. Several...
Journal of the American Helicopter Society
28th Structures, Structural Dynamics and Materials Conference
ABSTRACT Application to the General Rotorcraft Aeromechanical Stability Program (GRASP) of new me... more ABSTRACT Application to the General Rotorcraft Aeromechanical Stability Program (GRASP) of new methodology for structural dynamic analysis, including substructuring, frames of reference, nodes, finite elements, and constraints, is discussed. The structure is decomposed into a hierarchy of substructures, and discrete relative motion between substructures is analyzed exactly. The finite element method is used to treat deformation of continua, and the library of finite elements includes a nonlinear beam element incorporating aeroelastic effects. Analytical bases for the aeroelastic beam element and the screw constraint are considered, and the important role of geometric stiffness in the formulation is shown.
1989 American Control Conference
14th Structures, Structural Dynamics, and Materials Conference
The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, canti... more The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and aero dynamic center axes is investigated for the hovering flight condition. The equations of motion are obtained by simplifying the general, nonlinear, partial differential equations of motion of an elastic rotating cantilever blade. The equations are adapted for a 1inear:zed stability analysis in the hovering flight condition by prescribing aerodynamic forces, applying Galerkin's method, and linearizing the resulting ordinary differential equations about the equilibrium operating con dition. The aerodynamic forces are obtained from strip theory based on a quasi-steady approxi mation of two-dimensional unsteady airfoil theory. Six coupled mode shapes, calculated from free vibration about the equilibrium operating condition, are used in the linearized stability analysis. The study emphasizes the effects of two types of structural coupling that strongly influence the stability of hingeless rotor blades. The first structural coupling is the linear coupling between flap and lead-lag bending of the rotor blade. A structural coupling parameter 6? is introduced to simulate variations in flap-lag structural coupling that arise for blades having nonuniform stiffness distributions. The second structural coupling is a nonlinear coupling between flap bending, lead-lag bending, and torsion deflections. Results are obtained for a wide variety of hingeless rotor configurations and operating conditions in order to provide a reasonably complete picture of hingeless rotor blade stability characteristics. The stability of torsionally flexible blades is strongly influenced by the effects of the bending-torsion sturctural coupling. Without precone, typical configurations are usually stable except for low values of 6? or low torsion frequencies. Addition of precone is strongly destabilizing for a wide range of configurations. Except for very low torsion frequencies, the results also indicate that the structural terms in the torsion equation dominate the torsion inertia and damping terms which permits the use of an approximate, but simplified, system of equations with fewer degrees of freedom. Finally, the accu racy of the results is sensitive to the number and type o f mode shapes used in the analysis.
19th AIAA Applied Aerodynamics Conference
A nonlinear aerodynamic methodology has been loosely coupled to a geometrically exact beam struct... more A nonlinear aerodynamic methodology has been loosely coupled to a geometrically exact beam structural analysis to study the static aeroelastic behavior of a high-aspect-ratio wing. The aim of the present effort was to investigate the effects of adding aerodynamic nonlinearity on the elastic behavior, in particular identifying the areas of nonlinearities and their importance. Care was taken to evaluate the Euler solver and the transfer of data between the aerodynamic and structural modules to identify sources of numerical error that may contribute to incorrect modeling of large deflections. It was found that sensitivities near the wing tip and leading edge required additional attention when clustering the computational aerodynamic grid near the surface. Further, the transfer of loads from the Euler code to the structural code requires that the nonlinear drop of forces and moments be modeled as exactly as possible. Otherwise errors in the predicted geometric deformations of up to 10% can occur. These are exacerbated for cases with large deflections and twist. For loosely coupled static aeroelastic simulations, the nonlinear aerodynamic predictions provided by the solution of the Euler equations are lower than the predictions of the vortex panel code. This results in lower predicted bending and twist by the higher-order aerodynamic code, indicating that the divergence and possibly flutter speeds predicted by lower-order aerodynamics may be overly conservative.
Journal of the American Helicopter Society
As part of an ongoing investigation into potential advantages of so-called fully intrinsic formul... more As part of an ongoing investigation into potential advantages of so-called fully intrinsic formulations, this paper presents an application of the fully intrinsic equations of motion and kinematics for beams to rotor blades. A fully intrinsic formulation is devoid of displacement and rotation variables. Although the governing equations are geometrically exact, they are free of the attendant singularities and infinite-degree nonlinearities found in other types of formulations. These nonlinear, first-order partial differential equations are suitable for analyzing initially curved and twisted, anisotropic beams and thus are very attractive for analysis of both helicopter and wind turbine blades. This two-part paper is devoted to the structural dynamics modeling of rotor blades with a wide variety of boundary conditions—in particular hingeless and bearingless rotor configurations. In Part I, the theory and the formulation are presented, along with verification of single-load-path config...
Recent Patents on Mechanical Engineering
International Journal of Non-Linear Mechanics
A non-linear theory is presented for stretching and inplane-bending of isotropic beams which have... more A non-linear theory is presented for stretching and inplane-bending of isotropic beams which have constant initial curvature and lie in their plane of symmetry. For the kinematics, the geometrically exact one-dimensional (1-D) measures of deformation are specialized for small strain. The 1-D constitutive law is developed in terms of these measures via an asymptotically correct dimensional reduction of the geometrically non-linear 3-D elasticity under the assumptions of comparable magnitudes of initial radius of curvature and wavelength of deformation, small strain, and small ratio of cross-sectional diameter to initial radius of curvature (h/R). The 1-D constitutive law contains an asymptotically correct refinement of O(h/R) beyond the usual stretching and bending strain energies which, for doubly symmetric cross sections, reduces to a stretch-bending elastic coupling term that depends on the initial radius of curvature and Poisson's ratio. As illustrations, the theory is applied to inplane deformation and buckling of rings and high arches. In spite of a very simple final expression for the second variation of the total potential, it is shown that the only restriction on the validity of the buckling analysis is that the prebuckling strain remains small. Although the term added in the refined theory does not affect the buckling loads, it is shown that non-trivial prebuckling displacements, curvature, and bending moment of high arches are impossible to calculate accurately without this term.
Rotorcraft technology is one of the most challenging, multidisciplinary and interdisciplinary pro... more Rotorcraft technology is one of the most challenging, multidisciplinary and interdisciplinary problems in engineering. For its sustained advancement requires a critical mass of researchers conducting interdisciplinary research in the four critical rotorcraft disciplines: aerodynamics, rotor dynamics & aeroelasticity, structures & materials, and flight mechanics & controls. To support and sustain this research requires a combination of analysis capabilities and experimental facilities, including the necessary research instrumentation. The Georgia Tech CERT has accumulated this critical mass of researchers and developed the necessary facilities with previous Army and Georgia Tech investments. The unique capabilities of rotorcraft (vertical flight & lifting capability, ability to operate from unprepared surfaces, low speed agility & maneuverability, etc.) make them essential weapon & support systems for the U.S. Army and other military services in the foreseeable future. Therefore, the problem studied is to sustain the advancement of rotorcraft technology by conducting leading edge research using sufficient research instrumentation for the direct benefit of future rotorcraft, as well as technology upgrades for existing rotorcraft. : < Vii) A
39th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit, 1998
Composite tilt rotor aeroelastic optimization is performed by using a published formulation of mi... more Composite tilt rotor aeroelastic optimization is performed by using a published formulation of mixed variational exact intrinsic equations of motion for dynamics of beams along with a finite-state dynamic inflow theory for rotors. A composite box beam model is used to represent the principal load carrying member of the rotor blade. The blade is discretized using finite elements. Each wall
17th Structures, Structural Dynamics, and Materials Conference, 1976
J Amer Helicopter Soc, 1991
Developments in Theoretical and Applied Mechanics, 1992
Journal of Guidance Control and Dynamics, 2000
Two major barriers to widespread US acceptance of offshore wind energy is reliability of rotor bl... more Two major barriers to widespread US acceptance of offshore wind energy is reliability of rotor blades and the difficulty to access for inspection and maintenance. This work presents operation and design strategies aimed to increase blade reliability and maximize power production. Operating strategies that prolong blade life while optimizing energy output allow for smarter maintenance planning and lower maintenance costs. Offshore plants require significant balance of station costs associated with each turbine, leading to large rotor diameters to capture the most energy per turbine. Rotor diameters have already approached 130 m, so this work extends that trend to 100 m blade (205 m diameter) designs. A combined aero/structural optimization process was used to produce new 100 m blade designs. A high-fidelity analysis method is presented to assess the local damage effects of a common damage type. The operation and design strategies are then compared for their effect to mitigate the loc...
Journal of Applied Mechanics, 2015
An asymptotic theory of composite plates is constructed using the variational asymptotic method. ... more An asymptotic theory of composite plates is constructed using the variational asymptotic method. To maximize simplicity and promote efficiency of the developed model, a transformation procedure is required to establish a mathematical link between an asymptotically correct energy functional derived herein and a simpler engineering model, such as a generalized Reissner–Mindlin model. Without relaxing the warping constraints and performing “smart minimization” or optimization procedures introduced in previous work, a different approach is suggested in this paper. To eliminate all partial derivatives of the 2D generalized strains in the asymptotically correct energy functional, a hybrid transformation procedure is systematically carried out by involving modified equilibrium and compatibility equations, and solving a system of linear algebraic equations via the pseudo-inverse method. Equivalent constitutive laws for the generalized Reissner–Mindlin plate model are then estimated. Several...
Journal of the American Helicopter Society
28th Structures, Structural Dynamics and Materials Conference
ABSTRACT Application to the General Rotorcraft Aeromechanical Stability Program (GRASP) of new me... more ABSTRACT Application to the General Rotorcraft Aeromechanical Stability Program (GRASP) of new methodology for structural dynamic analysis, including substructuring, frames of reference, nodes, finite elements, and constraints, is discussed. The structure is decomposed into a hierarchy of substructures, and discrete relative motion between substructures is analyzed exactly. The finite element method is used to treat deformation of continua, and the library of finite elements includes a nonlinear beam element incorporating aeroelastic effects. Analytical bases for the aeroelastic beam element and the screw constraint are considered, and the important role of geometric stiffness in the formulation is shown.
1989 American Control Conference
14th Structures, Structural Dynamics, and Materials Conference
The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, canti... more The stability of elastic flap bending, lead-lag bending, and torsion of uniform, untwisted, cantilever rotor blades without chordwise offsets between the elastic, mass, tension, and aero dynamic center axes is investigated for the hovering flight condition. The equations of motion are obtained by simplifying the general, nonlinear, partial differential equations of motion of an elastic rotating cantilever blade. The equations are adapted for a 1inear:zed stability analysis in the hovering flight condition by prescribing aerodynamic forces, applying Galerkin's method, and linearizing the resulting ordinary differential equations about the equilibrium operating con dition. The aerodynamic forces are obtained from strip theory based on a quasi-steady approxi mation of two-dimensional unsteady airfoil theory. Six coupled mode shapes, calculated from free vibration about the equilibrium operating condition, are used in the linearized stability analysis. The study emphasizes the effects of two types of structural coupling that strongly influence the stability of hingeless rotor blades. The first structural coupling is the linear coupling between flap and lead-lag bending of the rotor blade. A structural coupling parameter 6? is introduced to simulate variations in flap-lag structural coupling that arise for blades having nonuniform stiffness distributions. The second structural coupling is a nonlinear coupling between flap bending, lead-lag bending, and torsion deflections. Results are obtained for a wide variety of hingeless rotor configurations and operating conditions in order to provide a reasonably complete picture of hingeless rotor blade stability characteristics. The stability of torsionally flexible blades is strongly influenced by the effects of the bending-torsion sturctural coupling. Without precone, typical configurations are usually stable except for low values of 6? or low torsion frequencies. Addition of precone is strongly destabilizing for a wide range of configurations. Except for very low torsion frequencies, the results also indicate that the structural terms in the torsion equation dominate the torsion inertia and damping terms which permits the use of an approximate, but simplified, system of equations with fewer degrees of freedom. Finally, the accu racy of the results is sensitive to the number and type o f mode shapes used in the analysis.
19th AIAA Applied Aerodynamics Conference
A nonlinear aerodynamic methodology has been loosely coupled to a geometrically exact beam struct... more A nonlinear aerodynamic methodology has been loosely coupled to a geometrically exact beam structural analysis to study the static aeroelastic behavior of a high-aspect-ratio wing. The aim of the present effort was to investigate the effects of adding aerodynamic nonlinearity on the elastic behavior, in particular identifying the areas of nonlinearities and their importance. Care was taken to evaluate the Euler solver and the transfer of data between the aerodynamic and structural modules to identify sources of numerical error that may contribute to incorrect modeling of large deflections. It was found that sensitivities near the wing tip and leading edge required additional attention when clustering the computational aerodynamic grid near the surface. Further, the transfer of loads from the Euler code to the structural code requires that the nonlinear drop of forces and moments be modeled as exactly as possible. Otherwise errors in the predicted geometric deformations of up to 10% can occur. These are exacerbated for cases with large deflections and twist. For loosely coupled static aeroelastic simulations, the nonlinear aerodynamic predictions provided by the solution of the Euler equations are lower than the predictions of the vortex panel code. This results in lower predicted bending and twist by the higher-order aerodynamic code, indicating that the divergence and possibly flutter speeds predicted by lower-order aerodynamics may be overly conservative.
Journal of the American Helicopter Society
As part of an ongoing investigation into potential advantages of so-called fully intrinsic formul... more As part of an ongoing investigation into potential advantages of so-called fully intrinsic formulations, this paper presents an application of the fully intrinsic equations of motion and kinematics for beams to rotor blades. A fully intrinsic formulation is devoid of displacement and rotation variables. Although the governing equations are geometrically exact, they are free of the attendant singularities and infinite-degree nonlinearities found in other types of formulations. These nonlinear, first-order partial differential equations are suitable for analyzing initially curved and twisted, anisotropic beams and thus are very attractive for analysis of both helicopter and wind turbine blades. This two-part paper is devoted to the structural dynamics modeling of rotor blades with a wide variety of boundary conditions—in particular hingeless and bearingless rotor configurations. In Part I, the theory and the formulation are presented, along with verification of single-load-path config...
Recent Patents on Mechanical Engineering
International Journal of Non-Linear Mechanics
A non-linear theory is presented for stretching and inplane-bending of isotropic beams which have... more A non-linear theory is presented for stretching and inplane-bending of isotropic beams which have constant initial curvature and lie in their plane of symmetry. For the kinematics, the geometrically exact one-dimensional (1-D) measures of deformation are specialized for small strain. The 1-D constitutive law is developed in terms of these measures via an asymptotically correct dimensional reduction of the geometrically non-linear 3-D elasticity under the assumptions of comparable magnitudes of initial radius of curvature and wavelength of deformation, small strain, and small ratio of cross-sectional diameter to initial radius of curvature (h/R). The 1-D constitutive law contains an asymptotically correct refinement of O(h/R) beyond the usual stretching and bending strain energies which, for doubly symmetric cross sections, reduces to a stretch-bending elastic coupling term that depends on the initial radius of curvature and Poisson's ratio. As illustrations, the theory is applied to inplane deformation and buckling of rings and high arches. In spite of a very simple final expression for the second variation of the total potential, it is shown that the only restriction on the validity of the buckling analysis is that the prebuckling strain remains small. Although the term added in the refined theory does not affect the buckling loads, it is shown that non-trivial prebuckling displacements, curvature, and bending moment of high arches are impossible to calculate accurately without this term.
Rotorcraft technology is one of the most challenging, multidisciplinary and interdisciplinary pro... more Rotorcraft technology is one of the most challenging, multidisciplinary and interdisciplinary problems in engineering. For its sustained advancement requires a critical mass of researchers conducting interdisciplinary research in the four critical rotorcraft disciplines: aerodynamics, rotor dynamics & aeroelasticity, structures & materials, and flight mechanics & controls. To support and sustain this research requires a combination of analysis capabilities and experimental facilities, including the necessary research instrumentation. The Georgia Tech CERT has accumulated this critical mass of researchers and developed the necessary facilities with previous Army and Georgia Tech investments. The unique capabilities of rotorcraft (vertical flight & lifting capability, ability to operate from unprepared surfaces, low speed agility & maneuverability, etc.) make them essential weapon & support systems for the U.S. Army and other military services in the foreseeable future. Therefore, the problem studied is to sustain the advancement of rotorcraft technology by conducting leading edge research using sufficient research instrumentation for the direct benefit of future rotorcraft, as well as technology upgrades for existing rotorcraft. : < Vii) A
39th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference and Exhibit, 1998
Composite tilt rotor aeroelastic optimization is performed by using a published formulation of mi... more Composite tilt rotor aeroelastic optimization is performed by using a published formulation of mixed variational exact intrinsic equations of motion for dynamics of beams along with a finite-state dynamic inflow theory for rotors. A composite box beam model is used to represent the principal load carrying member of the rotor blade. The blade is discretized using finite elements. Each wall
17th Structures, Structural Dynamics, and Materials Conference, 1976
J Amer Helicopter Soc, 1991
Developments in Theoretical and Applied Mechanics, 1992
Journal of Guidance Control and Dynamics, 2000